1. Field of the Invention
The invention pertains to a vane designed to get oriented in the axis of an ambient airflow.
Such a vane is advantageously used in an aircraft probe designed to measure aerodynamic parameters of the ambient airflow of the aircraft.
2. Discussion of the Background
The piloting of any aircraft implies knowledge of the relative speed of the aircraft with respect to the ambient air, namely the relative wind. This speed is determined by means of sensors of static pressure po, the total pressure pt and the angle of incidence xcex1. The angle xcex1 gives the direction of the speed vector in a reference system related to the aircraft and ptxe2x88x92po gives the modulus of this speed vector. The three aerodynamic parameters are therefore used to determine the speed vector of an aircraft and subsidiarily a convertible or tilt-rotor aircraft.
One vane described in French patent FR 2 665 539 shows the utility of making the probe get oriented in the axis of the ambient airflow in order to facilitate the measurement of the angle of incidence. To overcome the frictional forces in the axis of rotation of the vane, that patent describes the use of a mechanical control loop system to cancel the aerodynamic incidence of the vane. That control loop system is useful above all at the low speeds of ambient air flow because, the lower the speed, the weaker are the aerodynamic forces of air on the vane, which do not suffice to overcome the mechanical frictional forces to orient the vane accurately in the axis of the ambient airflow. The use of the control loop system based on the cancelling of the aerodynamic incidence of the vane, however, has one drawback. In practice, the inevitable imperfections in the making of the vane create an angular divergence between the orientation of the vane due to the aerodynamic forces at high airflow speeds and the orientation of the vane due to the control loop at the low airflow speeds. Furthermore, at high airflow speeds, the control loop system may attempt to modify the orientation of the vane without being able to do so because of the size of the aerodynamic forces. This results in unnecessary consumption of electrical power by the control loop system.
The invention is aimed at overcoming these drawbacks by proposing a device that improves the consistency of the orientation of the vane whatever the speed of the ambient airflow.
To achieve this goal, an object of the invention is a vane device designed to get oriented in the axis of an ambient airflow and provided with means for the intake of differential pressure representing the aerodynamic incidence of the vane, characterized in that the intake of differential pressure is balanced when the vane is oriented naturally in the axis of the flow.
One advantage related to the invention is that it limits the cost of making the vane by preventing the narrowing of the tolerance values of shape, position, and dimension in the definition of the profile of the vane.
Another advantage related to the invention is that it prevents the introduction of corrections into the control loop parameters. Such corrections would hamper the interchangeability of the mobile blade of the vane alone, without its control loop means.